Image forming apparatus, image quality control method

ABSTRACT

A technique that can perform appropriate image quality control processing corresponding to fluctuation in a printing environment is provided. 
     An image forming apparatus that forms, on a sheet, a test pattern formed by a color obtained by mixing toners of plural colors, scans a test pattern image formed on the sheet with a color sensor, and performs predetermined image quality control processing on the basis of information scanned, the image forming apparatus including a media sensor that acquires information for discriminating a type of a sheet to be an object of image formation processing, a control-information acquiring unit that acquires, on the basis of the information acquired by the media sensor, information for control used in the image quality control processing, and a color sensor that is arranged further on a downstream side than a fixing device in a sheet conveying direction and scans the test pattern formed on the sheet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to image quality control processing in animage forming apparatus, and, more particularly to improvement ofaccuracy of the image quality control processing.

2. Description of the Related Art

In an image forming apparatus such as a color MFP, a gray image areaother than characters in an output image at the time of copy processingand print processing is often formed by mixing toners of four colors,yellow, magenta, cyan, and black. However, when the balance of tonerquantities of the respective colors is collapsed because of influencesof types of sheets onto which toner images are outputted, variation ofthe apparatus, and the like, this gray portion changes to a colored grayand is extremely deteriorated in appearance. Colors equal to or lower inorder than so-called secondary colors such as R, G, and B may alsochange to colors with a color balance collapsed depending on types ofoutput sheets because of a problem of transferability and the like. Whenthe color balance is collapsed in this way, conventionally, the colorbalance is adjusted using functions such as color balance adjustment.

However, since the color balance adjustment is manual adjustment, thecolor balance adjustment takes time. Even if the color balance isadjusted with effort, when a printer gamma characteristic fluctuatesbecause of aged deterioration and the like, the adjustment has to beperformed again every time the fluctuation occurs. Therefore, thecontrol is extremely complicated.

Moreover, even if the adjustment of the color balance is performed asdescribed above, since a type of a sheet as a recording medium ischanged commonly, in the conventional color balance adjustment method,it is practically difficult to accurately perform the adjustment of thecolor balance according to various situations.

SUMMARY OF THE INVENTION

It is an object of an embodiment of the invention to provide a techniquethat can perform appropriate image quality control processingcorresponding to fluctuation in a printing environment.

In order to solve the problems described above, an image formingapparatus according to an aspect of the invention is an image formingapparatus that forms, on a sheet, a test pattern formed by a colorobtained by mixing toners of plural colors, scans a test pattern imageformed on the sheet with a color sensor, and performs predeterminedimage quality control processing on the basis of information scanned.The image forming apparatus is characterized by including asheet-information acquiring unit that acquires information fordiscriminating a type of a sheet to be an object of image formationprocessing, a control-information acquiring unit that acquires, on thebasis of the information acquired by the sheet-information acquiringunit, information for control used in the image quality controlprocessing, and a color sensor that is arranged further on a downstreamside than a fixing device in a sheet conveying direction and scans thetest pattern formed on the sheet.

An image forming apparatus according to another aspect of the inventionis characterized by including a sheet-information acquiring unit thatacquires information for discriminating a type of a sheet to be anobject of image formation processing and a control-information acquiringunit that acquires, on the basis of the information acquired by thesheet-information acquiring unit, information for control used in theimage quality control processing.

An image forming apparatus according to still another aspect of theinvention is characterized by including sheet-information acquiringmeans for acquiring information for discriminating a type of a sheet tobe an object of image formation processing and control-informationacquiring means for acquiring, on the basis of the information acquiredby the sheet-information acquiring means, information for control usedin the image quality control processing.

An image quality control method according to still another aspect of theinvention is characterized by including a sheet-information acquiringstep of acquiring information for discriminating a type of a sheet to bean object of image formation processing and a control-informationacquiring step of acquiring, on the basis of the information acquired inthe sheet-information acquiring step, information for control used inthe image quality control processing.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing an internal structure of animage forming apparatus such as a digital color copying machine thatforms a copy image of a color image according to a first embodiment ofthe invention;

FIG. 2 is a block diagram schematically showing electrical connectionand a flow of a signal for control of the digital copying machine shownin FIG. 1;

FIG. 3 is a functional block diagram of the image forming apparatusaccording to the embodiment;

FIG. 4 is a diagram showing an example of a test pattern formed on asheet;

FIG. 5 is a conceptual diagram for explaining a method of correctinginformation for control in the embodiment; and

FIG. 6 is a flowchart for explaining a rough flow of processing (animage quality control method) in the image forming apparatus accordingto the embodiment described above.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the invention will be hereinafter explained withreference to the drawings.

First Embodiment

First, a first embodiment of the invention will be explained.

FIG. 1 schematically shows an internal structure of an image formingapparatus such as a digital color copying machine that forms a copyimage of a color image according to a first embodiment of the invention.This image forming apparatus is roughly constituted by a color scannerunit 1 as image scanning means for scanning a color image on an originaland a color printer unit 2 as image forming means for forming a copyimage of the color image scanned.

The color scanner unit 1 has an original stand 4 made of transparentglass that has an original stand cover 3 in an upper part thereof and isdisposed to be opposed to the original stand cover 3 in a closed stateand on which an original is set. Below the original stand 4, an exposurelamp 5 that lights an original placed on the original stand 4, areflector 6 for condensing light from the exposure lamp 5 onto theoriginal, a first mirror 7 that bends reflected light from the originalin a left direction with respect to the drawing, and the like aredisposed. The exposure lamp 5, the reflector 6, and the first mirror 7are fixed to a first carriage 8. The first carriage 8 is driven by anot-shown pulse motor to be translated along a lower surface of theoriginal stand 4.

On the left side in the figure with respect to the first carriage 8,i.e., in a direction in which light reflected by the first mirror 7 isguided, a second carriage 9 provided to be movable in parallel to theoriginal stand 4 via a not-shown driving mechanism (e.g., a toothed beltand a DC motor) is disposed. In the second carriage 9, a second mirror11 that bends the reflected light from the original guided by the firstmirror 7 downward in the figure and a third mirror 12 that bends thereflected light from the second mirror 11 in the right direction in thefigure are arranged at a right angle to each other. The second carriage9 is driven by the first carriage 8 and translated along the originalstand 4 at a speed half of that of the first carriage 8.

In a plane including an optical axis of the light returned by the secondand the third mirrors 11 and 12, a focusing lens 13 that focuses thereflected light from the third mirror 12 at a predeterminedmagnification is arranged. In a plane substantially orthogonal to theoptical axis of the light transmitted through the focusing lens 13, aCCD color image sensor (a photoelectric conversion element) 15 thatconverts the reflected light imparted with a focusing property by thefocusing lens 13 into an electric signal is disposed.

When the light from the exposure lamp 5 is condensed onto the originalon the original stand 4 by the reflector 6, reflected light from theoriginal is made incident on the color image sensor 15 via the firstmirror 7, the second mirror 11, the third mirror 12, and the focusinglens 13. In the color image sensor 15, the incident light is convertedinto electric signals corresponding to three primary colors of light,i.e., R (red), G (green), and B (blue).

The color printer unit 2 has first to fourth image forming units 10 y,10 m, 10 c, and 10 k that form images subjected to color separation foreach of color components on the basis of the well-known subtractivecolor mixture process, i.e., images of four colors of yellow (y),magenta (m), cyan (c), and black (k).

Below the respective image forming units 10 y, 10 m, 10 c, and 10 k, aconveying mechanism 20 including a conveyor belt 21 as conveying meansfor conveying the images of the respective colors formed by therespective image forming units in an arrow “a” direction in the figureis disposed. The conveyor belt 21 is wound around and tensed between adriving roller 91 rotated in the arrow “a” direction by a not-shownmotor and a driven roller 92 spaced a predetermined distance apart fromthe driving roller 91. The conveyor belt 21 is caused to endlesslytravel in the arrow “a” direction at a constant speed. The respectiveimage forming units 10 y, 10 m, 10 c, and 10 k are disposed in seriesalong the conveying direction of the conveyor belt 21.

The respective image forming units 10 y, 10 m, 10 c, and 10 k includephotoconductive drums 61 y, 61 m, 61 c, and 61 k as image bearingmembers, outer peripheral surfaces of which are formed to be rotatablein an identical direction in positions in contact with the conveyor belt21, respectively. The respective photoconductive drums 61 y, 61 m, 61 c,and 61 k are driven at a predetermined speed by a not-shown motor.

The respective photoconductive drums 61 y, 61 m, 61 c, and 61 k aredisposed such that axes thereof are set at equal intervals from oneanother. The axes are disposed to be orthogonal to the direction inwhich the images are conveyed by the conveyor belt 21. In the followingexplanation, an axial direction of the respective photoconductive drums61 y, 61 m, 61 c, and 61 k is set as a main scanning direction (a seconddirection) and a rotating direction of the photoconductive drums 61 y,61 m, 61 c, and 61 k, i.e., a rotating direction of the conveyor belt 21(the arrow “a” direction in the figure) is set as a sub-scanningdirection (a first direction).

Around the respective photoconductive drums 61 y, 61 m, 61 c, and 61 k,charging devices 62 y, 62 m, 62 c, and 62 k as charging means extendedin the main scanning direction, charge removing devices 63 y, 63 m, 63c, and 63 k, developing rollers 64 y, 64 m, 64 c, and 64 k as developingmeans also extended in the main scanning direction, lower agitatingrollers 67 y, 67 m, 67 c, and 67 k, upper agitating rollers 68 y, 68 m,68 c, and 68 k, transferring devices 93 y, 93 m, 93 c, and 93 k astransferring means also extended in the main scanning direction,cleaning blades 65 y, 65 m, 65 c, and 65 k also extended in the mainscanning direction, and waste-toner collecting screws 66 y, 66 m, 66 c,and 66 k are arranged in order along the rotating direction of thephotoconductive drums 61 y, 61 m, 61 c, and 61 k, respectively.

The respective transferring devices 93 y, 93 m, 93 c, and 93 k aredisposed in positions for holding the conveyor belt 21 between thetransferring devices 93 y, 93 m, 93 c, and 93 k and the photoconductivedrums 61 y, 61 m, 61 c, and 61 k corresponding thereto, i.e., on theinner side of the conveyor belt 21. Exposure points formed by anexposing device 50 described later are formed on the outer peripheralsurfaces of the photoconductive drums 61 y, 61 m, 61 c, and 61 k betweenthe charging devices 62 y, 62 m, 62 c, and 62 k and the developingrollers 64 y, 64 m, 64 c, and 64 k, respectively.

Below the conveying mechanism 20, sheet feeding cassettes 22 a and 22 bthat store plural sheets P as image forming media, onto which imagesformed by the respective image forming units 10 y, 10 m, 10 c, and 10 kare transferred, are arranged.

At one end of the sheet feeding cassettes 22 a and 22 b and on a sideclose to the driven roller 92, pickup rollers 23 a and 23 b that takeout the sheets P stored in the sheet feeding cassettes 22 a and 22 bfrom the top thereof one by one are arranged. Between the pickup rollers23 a and 23 b and the driven roller 92, registration rollers 24 foraligning a leading end of the sheet P taken out from the sheet cassette22 a or 22 b and a leading end of a yellow toner image formed on thephotoconductive drum 61 y of the image forming unit 10 y are arranged.On the right side in FIG. 1 of a housing of the image forming apparatusaccording to this embodiment, a manual feed tray 89 that makes itpossible to feed special paper such as backing paper and a long sheet isprovided.

In the manual feed tray 89, a media sensor 810 for detecting a type andthe like of a sheet (a sheet to be an object of image formationprocessing) set in the manual feed tray 89 is provided. It is possibleto provide the media sensor 801 not only in the manual feed tray 89 butalso in the sheet feeding cassettes 22 a and 22 b (see media sensors801′ shown in FIG. 1). In other words, it is preferable that the mediasensor 801 is arranged on a conveying path for a sheet on which a tonerimage is formed and in a position where a temporal margin enough forperforming predetermined image quality control processing can be securedfrom the time when a type of a sheet is detected until image formationprocessing for the sheet is performed. The media sensor 801 does notalways have to be arranged in the manual feed tray or the sheet feedingcassettes as long as the above conditions are satisfied. For example, itis also possible to reduce the number of arranged media sensors byarranging the media sensors in positions where all sheets fed from themanual feed tray and the sheet feeding cassettes pass (see the mediasensors 801′ shown in FIG. 1).

Toner images formed on the other photoconductive drums 61 y, 61 m, and61 c are supplied to respective transfer positions to be timed tocoincide with conveyance timing of the sheets P conveyed on the conveyorbelt 21.

Between the registration rollers 24 and the first image forming unit 10y and near the driven roller 92, i.e., substantially on the outerperiphery of the driven roller 92 across the transfer belt 21, anattracting roller 26 for giving an electrostatic attracting force to thesheet P conveyed at predetermined timing via the registration rollers 24is disposed. An axis of the attracting roller 26 and an axis of thedriven roller 92 are set to be parallel to each other.

At one end of the conveyor belt 21 and near the driving roller 91, i.e.,substantially on the outer periphery of the driving roller 91 across theconveyor belt 21, a positional deviation sensor 96 for detecting aposition of an image formed on the conveyor belt 21 is disposed.

The positional deviation sensor 96 is constituted by, for example, atransmission or reflection optical sensor.

On the outer periphery of the driving roller 91 and on the conveyor belt21 on a downstream side of the positional deviation sensor 96, aconveyor-belt cleaning device 95 for removing a toner adhering on theconveyor belt 21, paper dust of the sheet P, or the like is arranged.

In a direction in which the sheet P conveyed via the conveyor belt 21 isseparated from the driving roller 91 and further conveyed, a fixingdevice 80 that melts a toner image transferred on the sheet P by heatingthe sheet P to a predetermined temperature and fixes the toner image onthe sheet P is disposed. The fixing device 80 is constituted by a heatroller pair 81, oil applying rollers 82 and 83, a web winding roller 84,a web roller 85, and a web pressing roller 86. Further on the downstreamside than the fixing device 80 in the sheet conveying direction, a colorsensor 70 for optically scanning an image (in particular, a test patternimage described later) formed on a sheet is arranged. The sheet P havingthe toner image heated and fixed thereon in the fixing device 80 isdischarged by a paper discharge roller pair 87.

The exposing device 50 that forms electrostatic latent images subjectedto color separation on the outer peripheral surfaces of thephotoconductive drums 61 y, 61 m, 61 c, and 61 k, respectively, has asemiconductor laser oscillator 60 controlled to emit light on the basisof image data (Y, M, C, K) of the respective colors subjected to colorseparation by an image processing unit 36 that performs predeterminedimage quality control processing and the like. On an optical path of thesemiconductor laser oscillator 60, a polygon mirror 51 that reflects andscans laser beams and is rotated by a polygon motor 54 and fθ lenses 52and 53 for correcting a focus of the laser beams reflected via thepolygon mirror 51 and focusing the laser beams are provided in order.

Between the fθ lens 53 and the respective photoconductive drums 61 y, 61m, 61 c, and 61 k, first return mirrors 55 y, 55 m, 55 c, and 55 k thatbend the laser beams of the respective colors transmitted through the fθlens 53 to exposure positions of the respective photoconductive drums 61y, 61 m, 61 c, and 61 k and second and third return mirrors 56 y, 56 m,56 c, 57 y, 57 m, and 57 c that further bend the laser beams bent by thefirst return mirrors 55 y, 55 m, and 55 c are arranged.

The laser beam for black is returned by the first return mirror 55 k andthen guided onto the photoconductive drum 61 k without being bent by theother mirrors.

FIG. 2 shows a block diagram schematically showing electrical connectionand a flow of a signal for control of the digital copying machine shownin FIG. 1. In FIG. 2, a control system is constituted by three CPUs,namely, a main CPU (Central Processing Unit) 91 in a main control unit30, a scanner CPU 100 of the color scanner unit 1, and a printer CPU 110of the color printer unit 2.

The main CPU 31 performs bi-directional communication with the printerCPU 110 via a shared RAM (Random Access Memory) 35. The main CPU 31issues an operation instruction and the printer CPU 110 returns astatus. The printer CPU 110 and the scanner CPU 100 perform serialcommunication. The printer CPU 110 issues an operation instruction andthe scanner CPU 100 returns a status.

An operation panel 40 has a liquid crystal display unit 42, variousoperation keys 43, and a panel CPU 41 connected to the liquid crystaldisplay unit 42 and the operation keys 43. The operation panel 40 isconnected to the main CPU 31.

The main control unit 30 is constituted by the main CPU 31, a ROM (ReadOnly Memory) 32, a RAM 33, an NVRAM 34, a shared RAM 35, an imageprocessing unit 36, a page-memory control unit 37, a page memory 38, aprinter controller 39, and a printer font ROM 121.

The main CPU 31 manages overall control. The ROM 32 has a controlprogram and the like stored therein. The RAM 33 temporarily stores data.

The NVRAM (nonvolatile Random Access Memory: nonvolatile RAM) 34 is anonvolatile memory backed up by a battery (not shown) and holds storeddata even if a power supply is isolated.

The shared RAM 35 is used for performing bi-directional communicationbetween the main CPU 31 and the printer CPU 110.

The page-memory control unit 37 stores image information in and readsout the image information from the page memory 38. The page memory 38has an area that can store image information for plural pages. The pagememory 38 is formed to be capable of storing, for each page, dataobtained by compressing image information from the color scanner unit 1.

Font data corresponding to print data is stored in the printer font ROM121. The printer controller 39 expands printer data from an externalapparatus 122 such as a personal computer into image data at aresolution corresponding to data indicating a resolution given to theprint data using the font data stored in the printer font ROM 121.

The color scanner unit 1 is constituted by the scanner CPU 100 thatmanages overall control, a ROM 101 having a control program and the likestored therein, a RAM 102 for data storage, a CCD driver 103 that drivesthe color image sensor 15, a scanning motor driver 104 that controlsrotation of a scanning motor for moving the first carriage 8 and thelike, an image correcting unit 105, and the like.

The image correcting unit 105 is constituted by an A/D conversioncircuit that converts analog signals of R, G, and B outputted from thecolor image sensor 15 into digital signals, respectively, a shadingcorrection circuit for correcting fluctuation in a threshold level withrespect to the output signals from the color image sensor 15 due tovariation of the color image sensor 15, ambient temperature change, andthe like, a line memory that temporarily stores the digital signalssubjected to shading correction from the shading correction circuit, andthe like.

The color printer unit 2 is constituted by the printer CPU 110 thatmanages overall control, a ROM 111 having a control program and the likestored therein, a RAM 112 for data storage, a laser driver 113 thatdrives the semiconductor laser oscillator 60, a polygon motor driver 114that drives the polygon motor 54 of the exposing device 50, a conveyancecontrol unit 115 that controls conveyance of the sheet P by theconveying mechanism 20, a process control unit 116 that controlsprocesses for performing charging, development, and transfer using thecharging devices, the developing rollers, and the transferring devices,a fixing control unit 117 that controls the fixing device 80, an optioncontrol unit 118 that controls options, and the like.

The image processing unit 36, the page memory 38, the printer controller39, the image correcting unit 105, and the laser driver 113 areconnected by an image data bus 120.

FIG. 3 is a diagram showing functional blocks of the image formingapparatus according to this embodiment. The image forming apparatusaccording to this embodiment forms, on a sheet, a test pattern formed bya color obtained by mixing toners of plural colors, scans the testpattern formed on the sheet with a color sensor, and performspredetermined image quality control on the basis of information scanned.

As shown in the figure, the image forming apparatus according to thisembodiment includes, an image scanning unit 801, a color converting unit802, a gamma correction unit 803, output gradation processing unit 804,a printer engine 805, a control-information acquiring unit 806, asheet-information acquiring unit 807, a control-information generatingunit 808, and a setting-information acquiring unit 809.

The image scanning unit 801 is equivalent to the color scanner unit 1,the color converting unit 802, the gamma correction unit 803, and theoutput-gradation processing unit 804 are equivalent to the imageprocessing unit 36, the printer engine 805 is equivalent to the colorprinter unit 2, the control-information acquiring unit 806 and thecontrol-information generating unit 808 are equivalent to the main CPU31, the sheet-information acquiring unit 807 is equivalent to theprinter CPU 110, and the setting-information acquiring unit 809 isequivalent to the panel CPU 41.

The image scanning unit 801 is equivalent to the color sensor 70 or thecolor scanner unit 1. The color converting unit 802 performspredetermined color conversion processing. The gamma correction unit 803performs processing for correcting a gamma characteristic (an imageforming characteristic) (equivalent to predetermined image qualitycontrol processing) in the image forming apparatus. Image data subjectedto the gamma correction by the gamma correction unit 803 is outputted tothe printer engine 805 (the color printer unit 2) through theoutput-gradation processing unit 804.

The sheet-information acquiring unit 807 acquires information fordiscriminating a type of a sheet to be an object of image formationprocessing (smoothness of a sheet surface, a reflectance of the sheetsurface, an electric resistance of the sheet, thickness of the sheet, abase color of the sheet, etc.) from the media sensor 810 and the like.Information acquired by the media sensor 810 is transmitted to theprinter CPU 110.

The setting-information acquiring unit 809 acquires, from apredetermined memory area (e.g., the ROM 32 is adopted. Besides, it ispossible to adopt the RAM 33, the ROM 101, the RAM 102, the ROM 111, theRAM 112, the NVRAM 34, the shared RAM 35, and the like as thepredetermined memory area), setting information that is set concerningwhich of information acquired by the sheet-information acquiring unit807 and information acquired by the operation panel 40 is givenpriority.

The control-information generating unit 808 generates information forcontrol on the basis of the information acquired by thesheet-information acquiring unit 807 and predetermined information forgeneration. By calculating (generating) the information for control onthe basis of the information for generation such as a coefficient and afunction, it is possible to generate various kinds of information forcontrol corresponding to types of sheets while holding down a storagecapacity.

The main CPU 31 acquires information for control used for image qualitycontrol processing (e.g., a table for correction used for gammacorrection) on the basis of the information acquired by thesheet-information acquiring unit 807.

The control-information acquiring unit 806 acquires from the memory areaa table for control corresponding to the sheet, the information of whichis acquired, on the basis of the information acquired by thesheet-information acquiring unit 807 when at least one of the smoothnessof the surface, a material, and the base color of the sheet, theinformation of which is acquired, is different from that of a set sheet(that is, when the gradation characteristics of a sheet to be used varylargely). Here, an example in which the information for control is thetable for control is described. However, the information for control isnot limited to this. The information for control may be, for example, a“calculation function” for performing a numerical operation.

The control-information acquiring unit 806 can acquire the informationfor control used in the image quality control processing on the basis ofnot only information on detection by the media sensor 810 but also inputinformation received by the operation panel 40, information detected bya temperature sensor and a humidity sensor, and the like.

The control-information acquiring unit 806 acquires, when theinformation for discriminating a type of a sheet is received by theoperation panel 40, the information for control used in the imagequality control processing on the basis of the information acquired byone of the sheet-information acquiring unit 807 and the operation panel40 that is set to be given priority according to the setting informationacquired by the setting-information acquiring unit 809. Consequently,for example, when information of a sheet acquired by thesheet-information acquiring unit and information of a sheet manuallyinputted are different, it is possible to perform the image qualitycontrol processing with priority given to one of these kinds ofinformation according to contents of a prior setting. Specifically, itis possible to give priority to contents of manual input, for example,when a special sheet (e.g., a long sheet), detection of which isdifficult with the media sensor, is used.

Details of the processing in the image forming apparatus according tothis embodiment will be explained.

First, correction coefficients for performing correction of colors(gradation characteristics) are determined using the color sensor 70 fora standard output sheet as a reference determined in advance.

A test pattern is generated in the image forming apparatus and the testpattern formed on a sheet is scanned by the color sensor 70 to determinecorrection coefficients. FIG. 4 is a diagram showing an example of thetest pattern formed on the sheet.

On the basis of a result of detection by the color sensor 70, an amountof exposure and process conditions in the image forming apparatus, a“color conversion table” and a “gamma correction table” for convertingRGB signals in the image processing units into color reproduction areasof a color image forming apparatus (converting RGB signals into CMYKsignals), correction coefficients, and the like are calculated, or tablevalues and the like are acquired, and stored in a predetermined memoryarea.

Subsequently, correction coefficients of colors (gradationcharacteristics) are calculated for each of various sheets withdifferent thicknesses (thin paper, thick paper 1 thick paper 2, coatpaper, etc.), which are recommended sheets, and stored in thepredetermined memory area (see FIG. 5 described later).

When a user outputs an image to an arbitrary output sheet, if it isdetermined that a property of gradation characteristics of the sheet(color reproducibility by a toner) substantially changes on the basis ofan indication of thick paper by the user instruction or the detectionresult by the media sensor 801, the correction coefficients are switchedand color (output gradation) characteristics of the output image formedon the sheet are corrected using the correction coefficients(information for control) switched.

Second Embodiment

A second embodiment of the invention will be explained.

This embodiment is a modification of the first embodiment describedabove. In the following explanation, components same as those alreadydescribed in the first embodiment are denoted by the identical referencenumerals and signs and explanations of the components are omitted.

When a user outputs an image to an arbitrary output sheet, if anindication of thick paper by a user instruction or a sheet detected bythe media sensor 801 is different from a defined recommended sheet,correction coefficients adjusted to the output sheet are calculated. Thecorrection coefficients in this context are obtained by causing an imageforming apparatus to output a test pattern and recalculating correctioncoefficients. Consequently, it is possible to determine color (gradationcharacteristics) correction coefficients corresponding to the thicknessof the sheet and appropriately correct color (output gradation)characteristics of an output image.

Third Embodiment

A third embodiment of the invention will be explained.

This embodiment is a modification of the first embodiment describedabove. In the following explanation, components same as those alreadydescribed in the first embodiment are denoted by the identical referencenumerals and signs and explanations of the components are omitted.

FIG. 5 is a conceptual diagram for explaining a method of generatinginformation for control in this embodiment.

First, in this embodiment, gamma automatic control is applied torecommended sheets to calculate a recommendation table. Then, as in theembodiment described above, correction tables of sheets such as “thickpaper” and “coat paper” in the case in which the sheets are therecommended sheets are estimated on the basis of correction tables ofthe recommended sheets. Estimation processing in this context isperformed by calculating, using a coefficient, a function, and the like,a correction table corresponding to a sheet as an object with respect toa correction table of a sheet as a reference.

The processing is effective because it is possible to generate acorrection table even if there is no “thick paper” and “coat paper”actually. For example, when it is possible to actually perform gammaautomatic control processing for the “thick paper 1”, by replacing acorrection table obtained by the automatic control with a correctiontable estimated for the thick paper 1, it is possible to obtain acorrection table accurately reflecting a state of sheets and contributeto improvement of accuracy of image quality control processingcorresponding to various recording media.

FIG. 6 is a flowchart for explaining a rough flow of processing (animage quality control method) in the image forming apparatus accordingto the embodiment described above.

The operation panel 40 receives an operation input of the user (anoperation inputting step) (S101).

The panel CPU 41 acquires, from the operation panel 40, settinginformation concerning which of information in a sheet-informationacquiring step and information in the operation inputting step is givenpriority (a setting-information acquiring step) (S102).

The printer CPU 110 acquires information for discriminating a type of asheet to be an object of image formation processing (thesheet-information acquiring step) (S103).

The main CPU 31 generates information for control on the basis of theinformation acquired in the sheet-information acquiring step andpredetermined information for generation (a control-informationgenerating step) (S104).

The main CPU 31 acquires information for control (e.g., a table forcontrol) used for image quality control processing on the basis of theinformation acquired in the sheet-information acquiring step (acontrol-information acquiring step) (S105).

In the control-information acquiring step, a table for controlcorresponding to the sheet, the information of which is acquired, isacquired on the basis of the information acquired in thesheet-information acquiring step when at least one of smoothness of thesurface, a material, and a base color of the sheet, the information ofwhich is acquired, is different from that of a set sheet.

In the control-information acquiring step, the information for controlused in the image quality control processing is acquired on the basis ofinput information received in the operation inputting step.

It is preferable that, in the control-information acquiring step, wheninformation for discriminating a type of a sheet is received in theoperation inputting step, the information for control used in the imagequality control processing is acquired on the basis of the informationacquired in one of the sheet-information acquiring step and theoperation inputting step that is set to be given priority according tothe setting information acquired in the setting-information acquiringstep.

As described above in this embodiment, it is desirable that gammacorrection for gradation characteristics is performed using arecommended sheet as a reference and, for other kinds of sheets,correction tables are obtained by calculation. Coefficients and the likeset in advance are used when a sheet to be used is a recommended sheet.When the sheet is changed to another sheet, the image forming apparatusis caused to output a test pattern in order to calculate a coefficient.In this way, the gradation characteristics are changed to gradationcharacteristics adjusted to the sheet.

The respective steps in the processing (the image quality controlmethod) in the image forming apparatus described above are realized bycausing the CPUs (the main CPU 31, the panel CPU 41, the scanner CPU100, and the printer CPU 110) to execute an image quality controlprogram stored in the memories (the ROM 32, the RAM 33, the ROM 101, theRAM 102, the ROM 111, the RAM 112, the NVRAM 34, and the shared RAM 35).

In the embodiments described above, the example is cited in which thepredetermined image quality control processing is the gamma correctionprocessing. However, the invention is not limited to this. It ispossible to apply the invention to image quality control processing aslong as it is necessary change processing contents according to a typeof a recording medium in the image quality control processing.

In the embodiments described above, the example is cited in which therecording medium, on which an image is formed, is a copy sheet or thelike. However, the invention is not limited to this. It is possible toadopt any sheet as long as the sheet is a sheet on which it is possibleto form an image such as thick paper and an OHP film.

In this embodiment, the functions for carrying out the invention arerecorded in the apparatus in advance. However, the invention is notlimited to this. The same functions may be downloaded from a network tothe apparatus or the same functions stored in a recording medium may beinstalled in the apparatus. As the recording medium, a form of therecording medium may be any form as long as the recording medium is arecording medium that can store programs and is readable by theapparatus such as a CD-ROM. The functions obtained by installation ordownload in advance in this way may be realized in cooperation with anOS (Operating System) or the like in the apparatus.

The invention has been explained in detail according to the specificforms. However, it would be obvious for those skilled in the art thatvarious alterations and modifications can be made without departing fromthe spirit and the scope of the invention.

As described in detail above, according to the invention, it is possibleto provide a technique that can perform appropriate image qualitycontrol processing corresponding to fluctuation in a printingenvironment.

1. An image forming apparatus, comprising: a sheet-information acquiringunit configured to acquire information for discriminating a type of asheet to be an object of image formation processing; an operationinputting unit configured to receive an operation input of a user; acontrol-information acquiring unit configured to acquire information forcontrol used in the image quality control processing on the basis of theinformation acquired by the sheet-information acquiring unit or on thebasis of input information received by the operation inputting unit; anda setting-information acquiring unit configured to acquire settinginformation concerning which of information of the sheet-informationacquiring unit and information of the operation inputting unit is givenpriority, wherein the control-information acquiring unit acquires, whenthe information for discriminating the type of the sheet is received bythe operation inputting unit, the information for control used in theimage quality control processing on the basis of the informationacquired by one of the sheet-information acquiring unit and theoperation inputting unit that is set to be given priority according tothe setting information acquired by the setting-information acquiringunit.
 2. An image forming apparatus according to claim 1, wherein theinformation for control is a table for control, and thecontrol-information acquiring unit acquires a table for controlcorresponding to the sheet, the information of which is acquired, on thebasis of the information acquired by the sheet-information acquiringunit when at least one of smoothness of a surface, a material, and abase color of the sheet, the information of which is acquired, isdifferent from that of a set sheet.
 3. An image forming apparatusaccording to claim 1, Wherein the sheet-information acquiring unit is amedia sensor that detects at least one of smoothness of a sheet surface,a reflectance of the sheet surface, an electric resistance of the sheet,thickness of the sheet, and a base color of the sheet.
 4. An imageforming apparatus according to claim 1, comprising a control-informationgenerating unit configured to generate the information for control onthe basis of the information acquired by the sheet-information acquiringunit and predetermined information for generation.
 5. An image qualitycontrol method, comprising: acquiring information for discriminating atype of a sheet to be an object of image formation processing; receivingan operation input of a user; acquiring information for control used inthe image quality control processing on the basis of the informationacquired in the step of acquiring information or on the basis of inputinformation received by the step of receiving an operation input; andacquiring setting information concerning which of information in thestep of acquiring information and information in the step of receivingan operation input is given priority, wherein in the step of acquiringinformation for control, when the information for discriminating thetype of the sheet is received in the step of receiving an operationinput, the information for control used in the image quality controlprocessing is acquired on the basis of the information acquired in oneof the step of acquiring information and the step of receiving anoperation input that is set to be given priority according to thesetting information acquired in the step of acquiring settinginformation.
 6. An image quality control method according to claim 5,wherein, in the step of acquiring information, at least one ofsmoothness of a sheet surface, a reflectance of the sheet surface, anelectric resistance of the sheet, thickness of the sheet, and a basecolor of the sheet is detected.
 7. An image quality control methodaccording to claim 5, comprising the step of generating the informationfor control on the basis of the information acquired in the step ofacquiring information and predetermined information for generation. 8.An image quality control method according to claim 5, wherein theinformation for control is a table for control, and in the step ofacquiring information for control, a table for control corresponding tothe sheet, the information of which is acquired, is acquired on thebasis of the information acquired in the step of acquiring informationwhen at least one of smoothness of a surface, a material, and a basecolor of the sheet, the information of which is acquired, is differentfrom that of a set sheet.
 9. An image forming apparatus, comprising:sheet-information acquiring means configured to acquire information fordiscriminating a type of a sheet to be an object of image formationprocessing; operation inputting means configured to receive an operationinput of a user; control-information acquiring means configured toacquire information for control used in the image quality controlprocessing on the basis of the information acquired by thesheet-information acquiring means or on the basis of input informationreceived by the operation inputting means; and setting-informationacquiring means configured to acquire setting information concerningwhich of information of the sheet-information acquiring means andinformation of the operation inputting means is given priority, whereinthe control-information acquiring means acquires, when the informationfor discriminating the type of the sheet is received by the operationinputting means, the information for control used in the image qualitycontrol processing on the basis of the information acquired by one ofthe sheet-information acquiring means and the operation inputting meansthat is set to be given priority according to the setting informationacquired by the setting-information acquiring means.
 10. An imageforming apparatus according to claim 9, comprising control-informationgenerating means configured to generate the information for control onthe basis of the information acquired by the sheet-information acquiringmeans and predetermined information for generation.
 11. An image formingapparatus according to claim 9, wherein the information for control is atable for control, and the control-information acquiring means acquiresa table for control corresponding to the sheet, the information of whichis acquired, on the basis of the information acquired by thesheet-information acquiring means when at least one of smoothness of asurface, a material, and a base color of the sheet, the information ofwhich is acquired, is different from that of a set sheet.
 12. An imageforming apparatus according to claim 9, wherein the sheet-informationacquiring means is a media sensor that detects at least one ofsmoothness of a sheet surface, a reflectance of the sheet surface, anelectric resistance of the sheet, thickness of the sheet, and a basecolor of the sheet.